1. Field of the Invention
This invention relates to redundancy approaches for magnetic bubble domain chips, and more particularly to a method of diagnosing and repairing a magnetic bubble domain chip.
2. Description of the Prior Art
Complete magnetic bubble domain systems including read, write and storage functions are known in the art as evidenced by U.S. Pat. No. 3,701,124. In the instant application, a magnetic "chip" will be defined as a magnetic bubble domain medium capable of supporting magnetic bubble domains therein, together with associated circuitry for providing routine functions (such as read, write and storage) in the magnetic bubble domain medium.
Calculations have been made which indicate that, for bubble domain bit capacities greater than 10.sup.5 bits, the yield of perfect chips begins to decrease rapidly. Thus, an approach which would allow a magnetic chip with a small number of malfunction areas to repair itself and remain operational would be of significant value. In the prior art, copending application Ser. No. 249,026, filed May 1, 1972, now abandoned describes a magnetic bubble domain system having redundancy. In that application, on-chip redundancy is provided using spare storage units as well as units which give a spare storage unit the personality of a faulty storage unit to be replaced. Specifically, structure is provided to physically remove connections in order to substitute a spare storage unit (such as a shift register) for a faulty storage unit. The spare storage units are provided with spare decoders as well as spare sensing means.
Other known prior art consists of U.S. Pat. No. 3,792,450 to Bogar et al. The structure involved in this patent comprises a magnetic bubble domain chip utilizing a major/minor loop configuration. Defective minor loops are determined by the absence of emerging bubble domains which are in turn utilized to create a program on a separate loop. This program is then used to determine which minor loops are to be used. Considerable structure and control, as well as a dedicated loop, are required. Further, entrance of domains into defective loops is not otherwise inhibited. Should a defect exist in the program, then stored data will become worthless.
The present invention differs from the prior art and the above cross-referenced application in that dynamic testing procedures can be used to provide a defect-tolerant magnetic chip in a very short time.